Gyratory crushers are used for crushing ore, mineral and rock material to smaller sizes. Typically, the crusher comprises a crushing head mounted upon an elongate main shaft. A first crushing shell is mounted on the crushing head and a second crushing shell is mounted on a frame such that the first and second crushing shells define together a crushing gap through which the material to be crushed is passed. A driving device is arranged to rotate an eccentric assembly arranged about the lower portion of the shaft so as to cause the crushing head to perform a gyratory pendulum movement and crush the material introduced in the crushing gap.
So as to replace the crushing shell mounted on the head, the crushing head, also commonly referred to as a head centre, is typically formed with means for attachment to a lifting mechanism so that the head centre and the shell may be lifted vertically upward via a crane. The wear parts may then replaced and any maintenance work performed within the crushing chamber. U.S. Pat. No. 5,323,976 discloses a cone shaped head centre having a series of holes formed in an upper end of the cone body to receive bolts for mounting brackets that are engageable by hooks of a lifting crane to remove the head vertically upward from the chamber.
These bore holes located in the very upper end of the crushing head are subject to high tangential stresses resultant from the head manufacturing process. Additionally, the holes at this location act to generate significant stress concentrations which in certain situations give rise to stresses that exceed the yield strength of the materials from which the crushing head is formed. An alternative embodiment is described in U.S. Pat. No. 3,355,114 in which mounting projections extending radially outward from the outer surface of the head centre, with these projections positioned at a lower region of the head in the axial direction.
However, there is a need for a crushing head that is attachable to a suitable lifting assembly or apparatus that minimises tension stresses and stress concentrations when both in use and when engaged by lifting mechanisms.